Field of the Invention
The present invention relates to a laser processing machine capable of performing a perforating process by means of cutting applied to a sheet material and a perforating method utilizing such laser processing machine.
Description of Related Art
When it comes to formation of a hole of circumferentially closed shape in a sheet material W with the use of a laser processing machine, the conventional perforating method includes, as shown in FIG. 8 of the accompanying drawings, a process step A in which a sheet material portion Wa on an inner side of a processing route K following an inner periphery of a target hole H desired to be formed is perforated to define a pierced hole 20, a process step B in which cutting is applied radially from the pierced hole 20 to the processing route K, and a process step C in which cutting is carried out along the processing route K. In such a perforating method, since the processing route K is defined offset inwardly from an inner peripheral position of the hole H, the processing route tends to become an incompletely closed route, in which a process starting point Ps and a process terminating point Pe do not coincide with each other,
The process step B, too, is such that the process starting point is apt to displace towards a left side of the figure of FIG. 8 beyond B1 shown by the broken line. For this reason, a projection 21 protruding inwardly as shown in an enlarged diagram of FIG. 9 remains left in between the processing start point Ps and the processing terminating point Pe both defined in the inner periphery of the apertured hole H. If such a projection 21 remains left as discussed above, an inconvenience would occur in mounting of any other component in the hole H and, therefore, the projection 21 has to be eliminated at a later stage manually. Also, even though the completely closed route is formed in which in the processing route K the processing start position Ps and the processing terminating point Pe coincide with each other, it has been found that the projection 21 is left unremoved on a back surface side of the work W even though the projection 21 on an upper or front surface side of the work W is removed.
So that the above discussed projection 21 remains unremoved, a method has been suggested in which, as shown in FIG. 10 of the accompanying drawings, a processing start·terminating point Pse, at which the processing start point and the processing terminating point concurrently lie, is set on an outer side of the processing route K. In this respect, see the patent document 1 listed below. The presence of this suggested perforating method is effective to avoid any possible occurrence of the projections.